Among thermoplastic elastomers, styrene thermoplastic elastomers such as a styrene-butadiene block copolymer (SBS) and a styrene-isoprene block copolymer (SIS), which are block copolymers of a vinyl aromatic compound-a conjugated diene compound, are rich in flexibility and have good rubber elasticity and processability at normal temperature. Therefore, thermoplastic elastomer compositions containing these thermoplastic elastomers have been widely used as a substitute for vulcanized rubber.
Further, thermoplastic elastomer compositions using a hydrogenated block copolymer in which the double bond part of the block copolymers in the above thermoplastic elastomer compositions is hydrogenated have been further widely used as a substitute for vulcanized rubber because these compositions are improved in thermal aging resistance (thermal stability) and weather resistance.
However, the thermoplastic elastomer compositions using these hydrogenated block copolymers have a problem that there is still room to be improved in rubber properties, for example, oil resistance, a heat pressing deformation rate (compression set), and rubber elasticity at high temperatures.
Therefore, a crosslinked composition obtained by crosslinking a hydrogenated derivative of the above block copolymers is proposed as a composition in which the above characteristics are improved (for example, refer to Patent Literatures 1 to 5).
Many thermoplastic elastomer compositions obtained by dynamically crosslinking an olefin resin and an olefin copolymer rubber are also known.
For example, there are disclosed an elastomer composition obtained by dynamically crosslinking an ethylene copolymer resin such as an ethylene-vinylacetate copolymer and a rubber such as a halogenated butyl rubber (for example, refer to Patent Literature 6), an elastomer composition containing an EPDM rubber (ethylene-propylene-diene rubber) which is dynamically vulcanized in the presence of an ethylene copolymer resin such as an ethylene-vinylacetate copolymer (for example, refer to Patent Literature 7), an elastomer composition containing a halogenated butyl rubber or the like which is dynamically vulcanized in the presence of an ethylene-hexene copolymer and an ethylene-butene copolymer (for example, refer to Patent Literature 8), a composition containing a thermoplastic elastomer obtained by vulcanizing a mixture of an α-monoolefin copolymer rubber such as EPDM and crystalline polypropylene or the like and a low density ethylene-α-olefin copolymer (for example, refer to Patent Literature 9), a molded article obtained by blending a vulcanized EPDM and a crystalline ethylene polymer followed by free radical crosslinking treatment (for example, refer to Patent Literature 10), a composition containing a thermoplastic elastomer obtained by vulcanizing a mixture of EPDM and crystalline polypropylene, high density polyethylene, and low density polyethylene (for example, refer to Patent Literature 11), and an elastomer obtained by crosslinking treatment of a mixture of a crosslinkable rubber such as a terpolymer rubber, a thermoplastic resin such as polypropylene, and a highly fluid linear polyolefin processing additive (for example, refer to Patent Literature 12).
Further, there is proposed a thermoplastic elastomer composition which is excellent in compression set and molding processability in a high temperature region, flexible, and free from oil bleeding by obtained using an olefinic elastomer and a saturated styrenic elastomer (SEEPS or the like) in combination (for example, refer to Patent Literature 13).